The "No EQ" DSO Challenge!

[Filroden]

12 hours ago, Nigel G said:

Here's what I mean, these images are cropped from 135mm lens image to compare against 150p images.

They are all similar exposure times, the 135mm lens appears to gather more.

I don't detect much difference in the M42 shots. They have slightly different crops but looking closely at the area between M43 and the Running Man where I can only describe the Ha as forming a staircase between them. Both images are just starting to show this structure. There is a much more pronounced difference in the Flame/Horsehead image. As Neil says, I suspect this is for two reasons. I think you've got a lower black point in the image taken with the scope. Also, because the target covers far fewer pixels in the 135mm (it has the larger field of view by some margin), each pixel will be "seeing" more photons so it will be easier/faster to capture (though the reflector's aperture will compensate to some extent).

[rotatux]

18 hours ago, Nigel G said:

Now my wife has agreed to let me build a summerhouse (observatory) at the bottom of our garden 100ft from the bungalow, which gives me 360 degree imaging field and be able to leave the mount set up.

Project for the coming months.

Good luck. A fixed observatory certainly alleviates the burden of EQ setup, when it's mostly done once. Hoping your observatory will get enough clear skies to enjoy.

[rotatux]

14 hours ago, Nigel G said:

Here's what I mean, these images are cropped from 135mm lens image to compare against 150p images.

They are all similar exposure times, the 135mm lens appears to gather more.

Pretty obvious indeed. IMO this helps to bring an answer to a long asked question about the equivalence between various apertures.

In all cases it's agreed that the bigger the (true) aperture, the more photons you get and the less exposure time you need. And the longer the focal length, the more magnifying and less photons (*) you get and the more exposure time you need. True aperture is focal / focal ratio, so 150mm for your scope and 48mm (2.8) or 39mm (3.5) for your lens.

(*) actually it's less photons per pixel, since the same quantity of photons flowing through the same aperture are just spread over a wider surface.

Question is by how much those two factors combine and compensate each other, and which one wins over the other. I've read many articles about it. Some say / demonstrate the captured light level per pixel is proportional to D²/F (or F/R², R being the focal ratio F/D), others say / demonstrate it's proportional to only D/F (= 1/R).

If the former was right, your scope (150²/750 = 30) should capture more light at the same sub length than your lens (135/2.8² = 17.2). Your shots seem to prove the latter is right, i.e. 1/5 < 1/3.5 or 1/2.8.

Of course post-processing vary, you should really compare out-of-sensors RAWs, or JPEGs processed strictly equally. But it also correlates with my own experience as a wide-field imager.

Edited February 7, 2017 by rotatux
asterisk about "less photons", 1/R equivalence

[rotatux]

19 hours ago, Nigel G said:

I have already got my Orion planetary imaging/guide cam and ordered the Orion mini 50mm guider scope, so will be able to guide as well.

BTW, is there such a thing as Alt-Az guiding ? Field rotation put apart, it could be a way to achieve longer subs. Or said otherwise, achieve subs as long as field rotation allows, without being annoyed with balancing or tracking errors. Thinking about it, that would severely impact transportability and ease of setup though (add laptop, guide scope+cam, cables, etc), but I wonder whether anyone has done it.

[SteveNickolls]

20 hours ago, Nigel G said:

Now my wife has agreed to let me build a summerhouse (observatory) at the bottom of our garden 100ft from the bungalow, which gives me 360 degree imaging field and be able to leave the mount set up.

Project for the coming months.

You lucky, lucky thing. All the very best with the build.

Cheers,
Steve

[Nigel G]

2 hours ago, rotatux said:

BTW, is there such a thing as Alt-Az guiding ? Field rotation put apart, it could be a way to achieve longer subs. Or said otherwise, achieve subs as long as field rotation allows, without being annoyed with balancing or tracking errors. Thinking about it, that would severely impact transportability and ease of setup though (add laptop, guide scope+cam, cables, etc), but I wonder whether anyone has done it.

I have been reading up on guiding and it can be done with an Alt-AZ mount, either with a camera rotator or the usual short exposure lengths, but I'm not sure its worth the cost of a guiding setup as your still limited to exposure times.

Most of the time the mount tracking is good enough for shorts.

Cassegrain Alt-AZ scopes seem to be more commonly used with guiding, for some reason.

My synscan handset has a ST4 port which can be connected to auto guiding

Cheers

Nige.

 

[happy-kat]

3 hours ago, rotatux said:

If the former was right, your scope (150²/750 = 30) should capture more light at the same sub length than your lens (135/2.8² = 17.2). Your shots seem to prove the latter is right, i.e. 1/5 < 1/3.5 or 1/2.8

Looks like my ST80 would capture pretty much the same as my 135mm if it's as above 80√ /400 but then you seem to include the aperture in the calculation?

[DarkD]

Interesting topic indeed !

Here is my contribution to the No EQ challenge

All images made with a SkyVision 16" Newton Alt-az with Stellarcat and skycommander .

No auto-guiding, no field rotator in action (althouh I have the Optec Pyxis LE), and 10" subs at 2000 ISO with Sony A7S (Astrodon inside)

Cheers

Michel

more pics here : http://nodinute.pagesperso-orange.fr/cp_ap_2016.html

 

[Filroden]

15 minutes ago, DarkD said:

All images made with a SkyVision 16" Newton Alt-az with Stellarcat and skycommander .

That's some light bucket! And it shows in the detail you've captured. I particularly like your M51 and M81/82 images. How do you find tracking with such a big beast?

[SteveNickolls]

13 hours ago, DarkD said:

Interesting topic indeed !

Here is my contribution to the No EQ challenge

All images made with a SkyVision 16" Newton Alt-az with Stellarcat and skycommander .

No auto-guiding, no field rotator in action (althouh I have the Optec Pyxis LE), and 10" subs at 2000 ISO with Sony A7S (Astrodon inside)

Just the job shows what a large objective can do; do you have a good, dark sky?

Cheers,
Steve

[rotatux]

20 hours ago, Nigel G said:

Cassegrain Alt-AZ scopes seem to be more commonly used with guiding, for some reason.

As Ken reminded us, the longer focal length requires more precision in tracking. I may just as well retry my MAK on small objects, as mine is somewhat shorter than Ken's.

 

19 hours ago, happy-kat said:

Looks like my ST80 would capture pretty much the same as my 135mm if it's as above 80√ /400 but then you seem to include the aperture in the calculation?

Yes aperture and/or focal ratio (also based on aperture). 80/400 is f/5 so you would have to close your 135 past 5 (e.g. f/5.6 and smaller) for your scope to bring you more photons on the sensor than the lens. Which you probably won't do, as most 135 are good enough from f/3.5 or f/4 (I dream I could find a f/2 one :-P).

[happy-kat]

Thank you

Is there a but, say both are at f5 won't the ST80 effectively bring me closer therefore more of the target covering more pixels of the longer focal length of the ST80. I'll have another play in the imaging tool using both and my camera, the ST80 will bring me closer I'll have to factor that in depending on target as it is too close really on m45.

[Filroden]

The way I think about it is that the target emits the same amount of photons they just land on more or less sensors depending on the field of view. The more sensors they land on the less photons per sensor, so the dimmer they will appear in the same time. So the target will appear smaller and brighter in the larger field of view. I think you're trading resolution for speed of capture.

Olly has a good graphic about the f-ratio myth that is much clearer.

[rotatux]

2 hours ago, happy-kat said:

Nice... I don't know that (Android) app, using Stellarium to plan my framing, what is it ?

[happy-kat]

SkySafari 4 plus, I have it for it's ability to control my virtuoso mount. Using on Android.

Thank you Ken I'll see if I can find Ollie's post.

[rotatux]

1 hour ago, Filroden said:

Olly has a good graphic about the f-ratio myth that is much clearer.

Maybe you mean that one ?

 

[DarkD]

22 hours ago, Filroden said:

That's some light bucket! And it shows in the detail you've captured. I particularly like your M51 and M81/82 images. How do you find tracking with such a big beast?

Thanks, tracking with stellarcat is really easy. You just have to initialize the system pointing two stars and you are ready for many hours of tracking. From Time to Time you can re-align on the object but just if you need the go-to.

[DarkD]

9 hours ago, SteveNickolls said:

Just the job shows what a large objective can do; do you have a good, dark sky?

Cheers,
Steve

Steve, unfortunately no ? Just an urban sky with to much light pollution. I will say M=4 to the naked eye at best. I have to move at least one hour from home to find a suitable dark sky... when imaging home I use the IDAS LPS filter... it helps but above 20s at 2000 iso and FD/4 the image is totally white ?

[SteveNickolls]

2 hours ago, DarkD said:

teve, unfortunately no ? Just an urban sky with to much light pollution. I will say M=4 to the naked eye at best. I have to move at least one hour from home to find a suitable dark sky... when imaging home I use the IDAS LPS filter... it helps but above 20s at 2000 iso and FD/4 the image is totally white ?

Sorry to hear that, it is around the same here, I can usually see to Mag 4.3. My only occasions for observing/imaging at darker sites are on family holidays when it's a pleasure to get to see the Milky Way. Good luck with your 16"-er and do keep posting!

Cheers,
Steve

[rotatux]

Two new pics finished (actually one has to stop somewhere), one half-success and another failed.

First is my #2 try at nebulas around Alnitak. Much better than my try #1, still progress to be done. I guess I can't catch more unless going to a darker site (was taken from Paris suburbs).

Capture: 101 good of 123 lights x 25s x 2500iso, 30 NG darks, Olympus E-PM1 with Skywatcher 130PDS on Celestron Nexstar SLT, Skywatcher ComaCorr and TS-UHC filter. Processing: Regim, Fotoxx.

Second is Rosette on which I failed to capture enough SNR (sorry for your eyes ;-)). I had to stretch so much I had to process the noise, even then the result isn't satisfying. Surely I was too ambitious when reducing the sub length to 20s, I suspect the UHC filter dims the overall image and requires at least 25-30s; Stars were burnt in my previous 30s try, so I decided to reduce it, but I might need HDR on it (or stop trying to image from Paris suburbs from which I can only barely see Orion's belt).

Capture: 50 good + 42 average lights (of 122) x 20s x 2500iso, 56 NG darks, Olympus E-PM1 with Skywatcher 130PDS on Celestron SLT mount, Skywatcher ComaCorr and TS UHC filter. Processing: Regim, Fotoxx.

A few days ago Ken gave me the idea to try to calibrate the color levels coming on the sensor through my filters, so I'm in the process of making some kind of flat in different filter configurations. Hoping to understand my filters characteristics and those bad star colors.

[The Admiral]

13 hours ago, rotatux said:

Two new pics finished (actually one has to stop somewhere), one half-success and another failed.

First is my #2 try at nebulas around Alnitak. Much better than my try #1, still progress to be done. I guess I can't catch more unless going to a darker site (was taken from Paris suburbs).

Capture: 101 good of 123 lights x 25s x 2500iso, 30 NG darks, Olympus E-PM1 with Skywatcher 130PDS on Celestron Nexstar SLT, Skywatcher ComaCorr and TS-UHC filter. Processing: Regim, Fotoxx.

Second is Rosette on which I failed to capture enough SNR (sorry for your eyes ;-)). I had to stretch so much I had to process the noise, even then the result isn't satisfying. Surely I was too ambitious when reducing the sub length to 20s, I suspect the UHC filter dims the overall image and requires at least 25-30s; Stars were burnt in my previous 30s try, so I decided to reduce it, but I might need HDR on it (or stop trying to image from Paris suburbs from which I can only barely see Orion's belt).

Capture: 50 good + 42 average lights (of 122) x 20s x 2500iso, 56 NG darks, Olympus E-PM1 with Skywatcher 130PDS on Celestron SLT mount, Skywatcher ComaCorr and TS UHC filter. Processing: Regim, Fotoxx.

A few days ago Ken gave me the idea to try to calibrate the color levels coming on the sensor through my filters, so I'm in the process of making some kind of flat in different filter configurations. Hoping to understand my filters characteristics and those bad star colors.

I'm not sure exactly what's going on here Fabien. Here's an image of the Rosette I made when I first got into astrophotography, and which was posted ages ago on this thread.

Now this was taken with a 102mm f7 refractor, so from an imaging point of view very similar to your set up. I used 130 x 10s lights, so about half the exposure you used. Admitedly, I'm not in the suburbs of a huge city, and I'm not using a pollution filter, and Orion's belt is clearly visible to me (at least, when this never ending cloud shifts out of the way!). I've found my camera to have a good red response, even though it is unmodified. May be your sky background is just too large. What effect the filter will have I don't know, as I've not used one, but one might hope it would give a significant improvement. It would be interesting to see what the deep red response of your camera is; this site might give you a clue https://kolarivision.com/articles/internal-cut-filter-transmission/, though it doesn't have your actual camera you may be able to identify others with the same sensor. Also, as a previous Olympus user (for general photography) I am aware that the MFT sensors are quite noisy, even the latest ones suffer a bit with long exposures. I fear you may be fighting against the odds here.

As for stars blowing out, I think that is to be expected with exposures used to capture the tenuous nebulosity, particularly with a sensor not specifically designed for well depth. Personally, I don't worry too much about it, and I think if you were to try HDR to capture them then the exposure differences needed would be quite large, much more than a 30s to 20s change would accommodate.

I guess the other alternative in your viewing location would be narrow band imaging, but that would require a dedicated camera such as the AS1600 4/3.

Ian

PS. You might be interested in this review which discusses noise levels in the EM5 and EM1 http://www.wrotniak.net/photo/m43/em1-em5-dark.html

Edited February 10, 2017 by The Admiral

[rotatux]

On 31/1/2017 at 16:57, The Admiral said:

I presume that you've read Craig Stark's article on "The Effect of Stacking on Bit-Depth"?  (http://www.stark-labs.com/craig/resources/Articles-&-Reviews/BitDepthStacking.pdf)

I found he brilliantly explains how stacking can get you additional bit depth (though there seems to be a off-by-one error in bit gains for each of his stacks).

(reading links from your last post, will follow up later ;-) )

[Filroden]

8 hours ago, The Admiral said:

Second is Rosette on which I failed to capture enough SNR (sorry for your eyes ;-)). I had to stretch so much I had to process the noise, even then the result isn't satisfying. Surely I was too ambitious when reducing the sub length to 20s, I suspect the UHC filter dims the overall image and requires at least 25-30s

I wonder if you've lost some of the data when removing/minimising the light pollution during processing? I found the Rosette, Soul and Orion Nebula all very difficult to process because they filled my field of view, making it difficult to calibrate any background gradient. Pacman was much easier as it occupied much less of the frame.

Here's two of my images of the Rosette - these are both from the same data (just one is rotated 180deg)! The biggest difference between them is that I improved my background model and preserved more of the nebula which existed in the unprocessed image.

[The Admiral]

34 minutes ago, Filroden said:

I wonder if you've lost some of the data when removing/minimising the light pollution during processing? I found the Rosette, Soul and Orion Nebula all very difficult to process because they filled my field of view, making it difficult to calibrate any background gradient. Pacman was much easier as it occupied much less of the frame.

Here's two of my images of the Rosette - these are both from the same data (just one is rotated 180deg)! The biggest difference between them is that I improved my background model and preserved more of the nebula which existed in the unprocessed image.

Not my post, gov! You are responding to Fabien's post.

Ian

[Nigel G]

I wonder if you add bias frames if it would help with noise levels.

You have captured a lot of data, it seems over powered by noise or light pollution. ( your loosing a lot during processing gradients ) maybe a lower ISO setting ?

Getting better though  

Nige.